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Much like seatbelt buckle sensor ICs, seat position sensor ICs commonly use a vane interrupt style of sensing to determine what zone, along the seat track, the seat is positioned. It includes a magnet and a unipolar, Hall-effect switch on either side of the seat track. When the seat itself slides into a predetermined zone, the ferrous material of a bar along the under part of the seat interrupts the path of the magnetic field to the sensing element, thereby switching the device on, and informing the airbag system that the seat is in that zone. Multiple sensor ICs can be used to determine different positions along the seat track, which can then be used by the airbag deployment controller to determine the relative position of the driver to the steering wheel or dashboard.
It is also common for seat position systems to utilize two-wire, unipolar, Hall-effect sensor ICs, because they require one less wire for operation and they provide inherent diagnostics (output current will be in one of two narrow ranges, any other value indicates conditions that may be a short, open or other type of fault).